1. Field of the Invention
The present invention relates generally to a gas insulated metal-clad high voltage equipment with an insulating bushing, and more particularly to a gas insulated metal-clad high voltage equipment provided with a single or a plurality of conductors disposed so as to pass through a grounded metal wall of a compartment and the insulating bushing filled with an insulating gas.
2. Description of the Prior Art
It is well knwon that dielectric strength of insulating gas or a mixture of insulating gas and air is greater than that of earth's atmosphere. Therefore, when high voltage devices for metal-clad power equipment are housed within a compartment filled with insulating gas, it is possible to reduce the size or the installation space of the power equipment.
In practice, however, it is usually impossible to house the whole high-voltage devices within the compartment filled with the insulating gas, because some devices should often be connected to or disconnected from another device installed outside the compartment or be checked in the outside for inspection or maintenance.
Taking the case of an enclosed switchgear as an example of gas insulation metal-clad power equipment, high voltage supply bus bars and load side bus bars are all housed within a grounded metal-clad bus compartment filled with insulating gas, but a circuit interrupter is installed outside the bus compartment in air. Therefore, in order to connect the devices housed within the bus compartment to those installed outside, some conductors should be disposed passing through the wall of the metal-clad compartment. The conductors should of course be insulated from the grounded compartment wall by appropriate insulating bushings. Various insulating bushings for insulating the conductor from the grounded compartment wall have been known. However, the size or dimensions of the insulating bushing are inevitably increased outside the bus compartment in order to prevent flashoever (dielectric breakdown on or along the surface of an insulator) from being generated between the conductor and the compartment wall within the surrounding air ambience. This is because flashover voltage is intended to be increased in dependence upon only an increase in flashover distance (distance along the surface of the insulator). Further, if the flashover distance is excessively increased, there exists another problem in that dielectric breakdown may occur between the conductor and the wall directly through inside the insulating bushing without occurrence of flashover along the surface of the insulator, thus it being impossible to effectively increase flashover voltage.
The advantage of the use of gas insulation metal-clad power equipment is to reduce the size of the equipment. However, this purpose is defeated when the dimensions of the insulating bushing are excessively great, thus resulting in high cost, heavy weight and large installation space requirements, etc.